Researchers at Brain teamed up with Boston University School of Medicine to analyze brain samples taken posthumously from 85 subjects, all of whom were former athletes, military veterans and civilians with a history of brain injuries.

“It’s the biggest report of its kind ever published,” said Dr. Robert Stern, one of the report’s authors and neurology professor at Boston University. “It doubles the world’s literature of cases of CTE (chronic traumatic encephalopathy).”

Eighty percent of the research subjects showed signs of CTE, a degenerative brain disease marked by headaches and loss of attention in stage one and depression, irritability, aggression, short term memory loss and heightened suicidal tendencies in later stages, the report said.

Thirty three of the 50 football players studied played in the NFL. Among the professional players were John Mackey, Ollie Matson and Cookie Gilchrist. Six played high school football and nine played college football. There were also seven boxers and four NHL players.

Still, researchers warn against making a direct connection between brain disease and head trauma as this report and others before it do not show definitively that sustained head trauma causes CTE.

While symptoms of CTE includes violence and depression, there is no evidence, Stern said, that the alleged murder-suicide that reverberated through the NFL this weekend could be linked to the condition. Kansas City Chiefs’ linebacker Jovan Belcher shot himself Saturday after allegedly shooting his girlfriend, prompting widespread speculation about what could have prompted the deadly violence.

“Suicide and murder suicide are amongst the most complex of human behaviors,” said Stern. “It’s not appropriate to jump to conclusions.”

The report demonstrates that the disease is found in people who have a history of repetitive brain trauma, Stern said. What it does not tell is what other factors contribute to the disease.

“Repetitive brain trauma is a necessary variable but it is not sufficient,” Stern said. “Not everyone in the sample had the disease and not everyone who gets hit in the head will get the disease.”

The research is still in its infancy and little is known about the disease itself, Stern said. Researchers are studying the types of hits, age, frequency, severity and genetic factors that contribute to CTE.

“My biggest hope is that adequate resources are provided for much needed research,” Stern said. “We need to prevent it, treat it and diagnose it during life.”